Is it actually over heating or could the gauge be bad?

Does it heat up in the highway, or just in traffic?

Was the HG replaced because of failure, did the over heating cause it to fail?

Definitely replace the t-stat w/an oem stock one, should cost under $15. Check the hoses(for squishiness), the water pump(for seepage) or replace if you don't know the age, check/replace the rad cap, it could be starting to fail. What is the age of the radiator?, it may need replacing or rebuilt.

What other mods do you have to your truck, i.e., exgaust tires, gears, etc.,? if you are running larger tires on stock gears, or have an open/too large exhaust, a cam wont make all that much of a difference.

The overheating issue shouldn't be too difficult to sort out. What dod the dealership do the first time you had it in?